Buenos Aires Police detained several protesters during clashes on Thursday morning after a bill to legalise abortion in the first 14 weeks of pregnancy was rejected by a narrow 38:31 vote.
Police barricaded the Senate and launched water cannons against protesters who hurled objects at them. Several detentions were made.
Senators rejected the bill by a seven vote margin, 38:31, with two abstentions.
The bill had not been supported by President Mauricio Macri.
Pro-choice supporters in Argentina had been rallied by legislative success in other predominantly Catholic countries such as Ireland, but in Latin America only three other states; Uruguay, Guyana and Cuba, permit early-term abortions.